248 DISCOVERY REPORTS 



The width of the nasopharynx was measured at the point where the pterygo-palatine 

 sutures most nearly approximate ; such measurements give an indication of the width 

 of the nasopharynx but naturally fail to show that in the female the ventral edge of the 

 pterygoid turns inwards towards the middle line, and, as one might say, rolls round on 

 itself, as age increases, whereas in the male the reverse happens, since the edges turn 

 outwards. The width of the soft palate thus decreases in the female but increases in 

 the male, relatively as well as absolutely, with advancing age. 



These characters are subject to a considerable degree of individual variation, but in 

 spite of this it is possible to sex well-grown skulls. With juvenile specimens, however, 

 it is difficult and often impossible, at any rate in the present state of knowledge. In very 

 young skulls there is the roundness common to all young animals, and the sexual 

 characters are very naturally not developed. The smallest male, no. 653, an animal about 

 a year old, shows a proportionately normal interorbital measurement but the zygomatic, 

 anterior frontal, maxillary and premaxillary measurements are all rather high compared 

 with the length of the skull (Table IV). In the juveniles of both sexes the pterygoids 

 are turned outwards, and in the females in proportion to the length of the skull the 

 interorbital bar is widest in the youngest specimens. 



As in body length so also in skull development the female departs farther from the 

 juvenile condition than the male; the former has typically larger crests than the latter 

 (this applies particularly to the sagittal crest), a more conspicuous narrowing of the 

 interorbital bar, and more massively developed jaws which produce a blunter muzzle, 

 and, finally, it is only in the large females that there is complete fusion of the palatine 

 sutures and of much of the nasal (vertical) wing of the premaxilla to the adjacent part 

 of the maxilla. Even in the largest males fusion of the premaxillae to the maxillae only 

 takes place in the alveolar region. 



The osteological changes due to increasing age are analogous in the two sexes, 

 except that, as stated above, they progress farther in the female. 



The specimens of each sex are divisible into four groups on grounds of size and 

 osteological characters, and since the former shows a progressive increase and the latter 

 a progressive ossification and development of crests, etc., it is inevitable that the four 

 stages represent stages in the development of the animal. Since it is established that 

 this species has a definite and limited pupping season it is reasonable to conclude that 

 all the seals of a given year will show common characters at any age up to sexual 

 maturity at least, and such definite groups as those mentioned above must be taken to 

 represent the first three years of life ; but in the absence of a much larger series than is 

 at present available it is not possible to subdivide the fourth, oldest, group which 

 therefore represents the fourth year and over. 



The following measurements were taken on each skull (see Figs, i and 2): 



(i) Total length, occipital condyle to tip of premaxillae. 



(2) Maximum zygomatic width (outside). 



(3) Minimum width of frontal bones (interorbital bar). 



(4) Maximum anterior width of frontals. 



